1. Field of the Invention
The present invention relates generally to a medical apparatus used during the performance of eye surgery, and in particular, is directed towards an improved suction ring, also termed a positioning assembly, for retaining, positioning and exposing a patient's eye for cutting of the cornea during a surgical procedure, such as to correct for refractive error. More specifically, the present invention is directed to an easily assembled and safe to use positioning assembly which minimizes the potential for improper cutting of the eyelid and/or eye, and further, which is capable of achieving and maintaining effective attachment on an eye, even one having a latitudinally narrowed ocular access, such as may be encountered in certain individuals, most notably, but not exclusively, children and persons of Asian descent.
2. Description of the Related Art
The eye works on a principle very similar to that of a camera wherein the iris, or colored portion of the eye about the pupil, functions like a shutter to regulate the amount of light admitted to the interior of the eye. The cornea or clear window of the eye, and the lens, which is located behind the pupil, serve to focus the light rays from an object being viewed onto the retina at the back of the eye. The retina then transmits the image of the object viewed to the brain via the optic nerve. Normally, these light rays will be focused exactly on the retina, which permits the distant object to be seen distinctly and clearly. Deviations from the normal shape of the corneal surface however, produce errors of refraction in the visual process so that the eye becomes unable to focus the image of the distant object on the retina, with the result that one sees a blurred image.
Many years ago, such refractive errors could only be treated with eyeglasses or contact lens, both of which have well known disadvantages for the user. Since then, however, surgical operations have been developed to change the refractive condition of the eye. Several methods and special instruments have been designed for performing this kind of surgery, which are primarily directed to reshape the cornea. It will be appreciated that the goal of corneal reshaping is to modify the curvature of the cornea, i.e., either to flatten or increase its curvature depending on the patient's condition, so that light rays passing through the cornea will thereafter be refracted to focus or converge directly onto the retina, thereby permitting the patient to view a distant object clearly.
One such surgical operation is keratomileusis, which requires a precise reshaping of the cornea by cutting and separating a thin layer of corneal tissue, termed the corneal cap, by lathing that tissue and then, by suturing the reshaped corneal tissue back into place on the eye. Keratomileusis is viewed, however, as having several drawbacks, and consequently, has been abandoned in recent years. Automated Lamellar Keratectomy (ALK) is another surgical technique which developed as an outgrowth of keratomileusis. In an ALK procedure, the eye is typically first numbed by a drop of anesthetic, and then, a device having a ring shaped configuration is placed on the eye to carefully position the cornea (termed "centration" in the art) for being cut by a very fine microsurgical instrument known as a microkeratome. The microkeratome is generally a blade carrying device that must be manually pushed or mechanically driven in a cutting path across the ring shaped device to cut into the cornea. Under an ALK procedure to treat near-sightedness, the microkeratome is typically first used to cut and lift a thin layer of the cornea, instead of severing it, and second, to carry out a reshaping of the cornea by way of a second pass of the microkeratome over the cornea with the cutting element adjusted to pass therethrough at a desired and pre-determined corrective depth. Thereupon the thin, raised layer of corneal tissue is put back in place over the cornea for healing.
There have been other significant developments in this field of art, however. For example, a procedure known as Laser Intrastromal Keratomileusis (LASIK), wherein a laser is utilized to re-shape and/or contour the cornea, is becoming increasingly accepted as both a safe, painless and rapidly effective procedure for correcting vision problems such as, but not limited to, nearsightedness, farsightedness and astigmatism, both regular and irregular. The LASIK procedure is currently considered optimal because it allows sculpting of the cornea without damaging adjacent tissues, and further, because with the aid of computers, the laser can be programmed by a surgeon to more precisely control the amount of tissue removed, and significantly, to permit more options for the reshaping of the cornea. Under LASIK procedures, the eye is still typically positioned within a ring shaped device and a microkeratome cutting head assembly is typically also used as a preliminary step to cut and raise a thin layer of corneal tissue in order to expose underlying portions of the eye for treatment with the laser. The cutting of a thin layer of corneal tissue is commonly known as a keratectomy, and in the most common case, a "corneal flap" will be cut, which leaves a hinged portion of tissue attached to the cornea, although there are special cases where a "free cap" is cut wherein the raised layer of corneal tissue is left detached from the eye.
Turning more specifically to how the eye is maintained in the desired position for a LASIK procedure, the ring shaped device referred to above is commonly used and is attached to the eyeball temporarily by way of a suctioning force or vacuum. As such, such devices are often referred to as suction rings, and a typical suction ring includes an annular, hollow ring that defines a central aperture, which allows the cornea to be exposed therethrough, and an open bottom side having a standard dimension and which is structured to engage the surface of the eye around the cornea. The suction ring is typically in communication with a hollow suction tube, which is in fluid flow communication with the open bottom side of the ring. A vacuum is commonly applied to such suction rings, via the suction tube, with a relative vacuum of typically between 20" Hg and 28" Hg, being applied, which draws the suction ring down upon the globe of the eye under the influence of external atmospheric pressure. As such, the suction ring attaches to the surface of the eyeball surrounding the cornea, with the suction force being applied and holding the ring in a reasonably secure fashion to the eyeball throughout the LASIK procedure. As a result, the suction ring has become a conventional device in ophthalmic practice, and it should be noted, is designed to be re-usable so as to accommodate a large number of patients over the course of its useful life.
While the use of such suction rings have become quite common in the art, there have been some drawbacks associated with them. For example, the configuration and size of known suction rings do not readily permit them to be comfortably and/or properly positioned within the ocular recess of many persons. More specifically, it has been determined that some individuals, and especially children and persons of Asian decent, tend to exhibit certain physical characteristics which result in there being a somewhat constricted area available for placement of the suction ring. For example, such individuals may either have a more narrow ocular recess and/or may not be able to open their eyes as wide as some other persons, especially in the latitudinal and/or up and down direction. This restricted access can often lead to difficulties for the practitioner performing a surgical procedure such as LASIK on the eye, as an insufficient surface area for proper securement of a traditional suction ring exists.
As a result, it would be highly beneficial to provide a microkeratome assembly, and in particular an improved suction ring for use with such an assembly, which is especially well suited for use in the eyes of all patients, including those having latitudinally smaller ocular accesses. Any such improved suction ring developed, however, should be able to be effectively and comfortably secured to the exposed portions of the patient's eye, while still exposing and presenting a sufficient depth and/or diameter of the cornea for cutting by the microkeratome cutting head assembly. Furthermore, if any such improved suction ring were developed, it would be very beneficial if it were structured for effective use with a cutting head assembly of the type configured to cut along an arcuate path, such as that disclosed in U.S. Pat. No. 5,624,456 and considered by many to perform a keratectomy with optimal results, without interfering with the cutting process and/or diminishing its accuracy, despite there being a more confined area or ocular recess.
It is also noted that conventional suction rings can be difficult to manufacture and/or assemble, particularly given the degree of precision which is necessary for safe and effective use during opthamological procedures. If a suction ring were developed which is suitable for a smaller ocular recess, which is commonly found on children and persons of Asian descent, these issues would also have to be addressed satisfactorily. Thus, it would be beneficial to provide an improved suction ring or positioning assembly which integrates all of the necessary components into an efficient, streamlined, and compact configuration, which is readily capable of being manufactured accurately and precisely, and which still allows for the safe and precise utilization of a microkeratome assembly. Lastly, it would also be beneficial if any improved suction ring were developed which could reasonably ensure that during a keratectomy, the microkeratome cutting head assembly will initiate cutting of the cornea at a uniform and rather precise position relative to the eyelid and/or cornea so as to avoid the possibility that an improper cut will occur. More in particular, it would be beneficial to provide an improved suction ring or positioning assembly that does not allow the cutting of an incision to begin unless the cutting head assembly is properly positioned.